Distribution

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I. triloba was originally a native of tropical America, but is now pantropical.

The map is based on published country records: I. triloba specimens have also been collected from Guatemala (R Westbrooks, Animal and Plant Health Inspection Service, USDA, North Carolina, USA, personal communication, 1995), the Lesser Antilles (Adams et al., 1972), Polynesia and Micronesia (Gunn and Ritchie, 1982).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Oceania

Risk of Introduction

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Seeds of I. triloba have been detected as a contaminant of sesame seeds originating from China, El Salvador and Guatemala (R Westbrooks, Animal and Plant Health Inspection Service, USDA, North Carolina, USA, personal communication, 1995). I. triloba has also been intercepted as a contaminant of various types of imported spices and as a 'hitch-hiker' in cars at the USA-Mexican border (Westbrooks, 1989).

Habitat

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I. triloba is known to occur in various habitats, including cultivated fields
(e.g., cotton, citrus groves), sandy ground and grassy swamp margins, on
hedges, and in thickets, from low to middle elevations (Ordetx, 1949; Haselwood
and Motter, 1966; Adams et al., 1972). In Queensland, Australia, it occurs as a
weed of sugarcane and tropical pastures (Auld and Medd, 1992). In Java, it has
been observed in brushwoods, living fences, sugarcane fields, roadsides,
fields, and waste places (van Ooststroom, 1965).

Habitat List

Biology and Ecology

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I. triloba is a twining annual herb that reproduces by seeds (Haselwood and Motter, 1966). Studies in the Philippines indicated that distinct patterns of emergence under natural conditions are related to rainfall patterns (Janiya and Moody, 1987).

In the Philippines, nicking the seed coat with a blade was the most effective dormancy-breaking treatment studied. Sand scarification was effective but damaged the seed. A 40-80% saturation level in the soil favoured germination (Gacutan, 1979).

I. triloba is considered to be an important plant in honey production in Cuba and other Central American countries (Ordetx, 1949).

Natural enemies

Notes on Natural Enemies

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The phytophagous arthropods (and their natural enemies) in an agroecosystem in
the warm region of central Tolima, Colombia were investigated from November
1976 until May 1979. This project found that Agrius cingulatus showed some
promise for biological control of I. triloba. On several occasions, this
sphingid completely defoliated the weed in soyabean crops without damaging the
crop. Larvae placed on soyabean leaves in the laboratory died without feeding
(Hallman, 1979).

Impact

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I. triloba is considered a serious weed in Australia and the Philippines; a
principal weed in Cuba, Hawaii, and Honduras; and a common weed in Argentina,
Jamaica, and Indonesia (Holm et al., 1979). Like other 'morning-glories', it
competes with crop plants for nutrients and water. Due to its twining nature,
it also fouls mechanical harvesters. It has been noted as one of three
morning-glory weeds of cotton fields in Arizona, USA (G Yatskievych, University
of Arizona, personal communication, 1981).

In Java, I. triloba is a weed of brushwoods, living fences, sugarcane fields,
roadsides, fields and waste places (van Ooststroom, 1965). A nematode
assessment survey of the vegetable-growing areas of Barangay Sicsican in
Talavera, Neuva, Ecija, Philippines found that I. triloba and several other
weeds serve as alternative hosts for root-knot nematodes (Meloidogyne javanica
and M. incognita). Such alternative hosts play an important role in the
nematodes' ability to survive and persist during the rice season before the
vegetable season (Mamari and Alberto, 1989).

In the Philippines, I. triloba is one of the main weeds of monoculture maize
(Pamplona, 1988), one of the most common weeds in intercropped maize, sorghum,
sunflowers, coconuts, tomatoes, and sesame (Moody, 1986), and has been listed
there as one of 21 common weeds of cotton (Paller and Lijauco, 1981).

In one study, varying densities of I. triloba were maintained in monocultures
of soyabeans or maize and maize-soyabean intercrops. Weed density did not
normally have a significant effect on insect pest populations, but the presence
of I. triloba tended to increase damage by insects in soyabeans and to act as a
pest attractant in maize (Mercado et al., 1980).

I. triloba was first reported in Israel in 1986 as a weed in cotton (Joel and
Liston, 1986).

Studies in the Solomon Islands showed that I. triloba and two other species are
alternative hosts for witches' broom disease of sweet potatoes (Jackson and
Zettler, 1983).

Detection and Inspection

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To avoid further worldwide spread, shipments of seeds and spices from infested
countries should be closely examined for the presence of seeds of I. triloba.
Devitalized [killed] seed samples should be provided to plant regulatory
inspectors to increase the effectiveness of the inspection. To avoid losses and
costs of control, field surveys should be conducted to permit early detection
and eradication of this noxious weed before it becomes firmly established.

Similarities to Other Species/Conditions

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According to Austin (1978), most floristic studies of the New World have failed
to recognize the difference between I. triloba and I. batatas (sweet potatoes).
Characteristics that separate these two species include corolla length [1.8-2
cm for I. triloba versus 3-5(7) cm], nectary colour (white versus yellow to
yellow-orange), number of seeds/fruit (four versus usually less than four),
and a lack of sweet potato tubers.

Another species that is similar to I. triloba is I. x grandifolia. According to
Austin (1978), these species may be separated by sepal shape (oblong to
narrowly elliptic-oblong for I. triloba versus lanceolate to ovate-lanceolate),
sepal length [6-8(10) mm versus 8-11 mm], capsule size (5-6 mm long and in
diameter versus 6-7 mm in diameter, capsule pubescence (pilose versus hirsute),
and seed size (2.5-3.2 mm long versus 3.5-4 mm long).

I. triloba and a rather common form of the hybrid I. x leucantha (parent
species I. lacunosa and I. trichocarpa) may be separated on the basis of sepal
shape (more or less oblong for I. triloba versus lanceolate), sepal length
[6-8(10) mm versus (8)10-14 mm], capsule size (5-6 mm long and in diameter
versus 7-8 mm in diameter), and seed size (2.5-3.2 mm long versus 3.2-4.5 mm
long) (Austin, 1978).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical, Cultural and Sanitary Methods

Coconuts
Research in the Philippines showed that I. triloba was controlled in coconut nurseries with the use of paraquat or by hand weeding at intervals of 1-2 months (Abad and Juan, 1981).

Maize
Field studies to evaluate different herbicides and herbicide combinations in the Philippines showed that pendimethalin alone failed to control I. triloba in maize cv. Pioneer 6181 (Jover et al., 1982). Madrid and Manimtim (1978a) found that atrazine provided good control of broad-leaved weeds, including I. triloba; however, oxyfluorfen provided good control for I. triloba but killed the maize.

Sugarcane and Sorghum
Research by the Hawaiian Sugar Planters' Association indicated that metsulfuron provided good control of I. triloba (Santo, 1989). In another Hawaiian study, conducted during the first 4-6 months of sugarcane growth until the canopy closed, atrazine was found to give excellent control of several broadleaved weeds, including I. triloba (Olney, 1971).

Field trials in sugarcane and sorghum in New South Wales and Queensland (Australia) during 1982-86, showed that I. triloba was moderately susceptible to fluroxypyr, but was controlled with a tank mixture of fluroxypyr and 2,4-D (Webb and Feez, 1987).

Hondrade (1981) found that pendimethalin was ineffective in controlling I. triloba in sugarcane.

In field trials in the Burdekin District of Queensland, 2,4-D and MCPA applied to sugarcane at hilling up gave good control of I. triloba, I. plebeia and I. purpurea, and provided an economical and reliable alternative to aerial spraying. The major Burdekin cane cultivars, Q96 and Q80, could be treated without risk of damage. 2,4-D was the least expensive of the treatments (on the basis of the cost of chemical). Extensive commercial spraying showed that 2,4,5,-T [superseded] could be used to maintain satisfactory weed control, but that higher rates were needed where Cucumis metuliferus or Passiflora subpeltata were also present (Anonymous, 1980).

Mungbeans and Soyabeans
In the Philippines, oxyfluorfen was effective in inhibiting the germination of I. triloba in mungbeans and soyabeans when applied 2 days after planting. Emergence of I. triloba was observed at lower rates, but the seedlings died 2 weeks after treatment (Fabro and Robles, 1982).

In another Philippine study, oxadiazon applied pre-emergence in soyabeans gave excellent control of I. triloba. In another trial, however, oxadiazon controlled I. triloba but severely injured the crop. Combination pre-emergence and post-emergence directed applications of bentazone also provided control (Madrid and Manimtim, 1978b).

Tomatoes and Cabbages
Rice straw, rice hulls and sawdust mulches reduced populations of I. triloba in tomatoes by 50% at 30 days after transplanting. However, the weed eventually penetrated the mulches and grew out of control. In transplanted cabbage, mulching also cut populations of I. triloba in half during the wet season of 1977 in the Philippines (Paller et al., 1979).

Miscellaneous
Pre-emergence application of bromacil was effective in controlling I. triloba in a variety of tropical crops in the Philippines (Mendoza, 1979). In another Philippine study, bentazone applied post-emergence or as a directed spray controlled I. triloba at the 2-3 leaf stage. However, yields were less than with hand weeding and weed control was not season long (Robles et al., 1979).

Biological Control

The phytophagous arthropods (and their natural enemies) in an agroecosystem in the warm region of central Tolima, Colombia were investigated from November 1976 until May 1979. This project found that Agrius cingulatus showed some promise for biological control of I. triloba. On several occasions, this sphingid completely defoliated the weed in soyabean crops without damaging the crop. Larvae placed on soyabean leaves in the laboratory died without feeding (Hallman, 1979).

Regulatory Control

I. triloba is listed as a Federal Noxious Weed in the USA. Introduction is permitted there only by permit from the Animal and Plant Health Inspection Service, USDA.

Preliminary studies indicate that a 0.35% solution of caustic soda (NaOH) in hot water at 92°C is sufficient to kill seeds of I. triloba that contaminate shipments of sesame (caustic soda is used to de-hull or decorticate raw sesame seeds). Preliminary studies also indicate that dry heat (hot air) temperatures of 130°C will kill seeds of I. triloba (R Westbrooks, Animal and Plant Health Inspection Service, USDA, North Carolina, USA, personal communication, 1995).

Regulatory strategies to prevent the world movement and further establishment of exotic pest plants such as I. triloba include foreign prevention (production of weed-free commodities for export to uninfested countries); exclusion (detection and mitigation of weed contaminants in imported products at ports of entry); detection, containments and eradication of incipient infestations, and cost-effective control of widespread species (Westbrooks, 1991).